Hunter brings the team the case of Marine Sgt. Marcos, a demolitions expert, who was just killed this morning in a blast while driving the SUV of an infamous club owner, Winslow, on an L.A freeway. Callen immediately questions Hunter on why this is their case and she just points out that they need no other reason than Marcos was a Marine. Additionally, Hunter decides to switch our team’s partners which just enrages Callen even more. Sam and Deeks head to Marcos home. When they arrive they see a man in the backyard running from a work shed, as they give chase the shed explodes. Sam takes down the man and once they take him to the boatshed, Sam and Callen interrogate him together – to Hunters annoyance – and discover he is Marcos’ friend and was the one who connected Marcos to Winslow. Winslow paid top dollar for Marcos to build five remote denotation bombs but after Marcos delivered the bombs he regretted it and was on his way to give Winslow back his money when he was murdered by one of his own bombs. Marcos’ friend, racked with guilt, volunteers to help Sam infiltrate Winslow’s organization to find out the target and stop him from detonating the bombs. They discover the target is the new club of Winslow’s former protégé turned rival. Callen and the team work to evacuate everyone within a one block radius while Sam works with Winslow inside pretending to help fix the bombs that Marcos supposedly rigged to be duds. Winslow catches on that the police may know what is going on and Marcos’ friend is killed in chaos as Winslow activates the bombs by accident. Sam rushes to find an exit as the building explodes.
Hunter sends Callen and Kensi on what appears to be a wild goose chase for Winslow’s girlfriend who doesn’t seem to exist. Nell finally finds a picture of her and shocks everyone when it is Agent Hunter. Callen rushes to confront Hunter and finds Hetty back in her office, seemingly aware of everything that has transpired under Agent Hunter while she was gone. Hetty tells Callen to sit down and gives him a piece of the puzzle to his past – his mother’s name